Metallic flux-cored welding wire and gas-shielded arc welding method

Abstract

To provide a metal flux-cored wire for welding that excels in welding workability and in resistance to pore defects and cracks, and also excels in mechanical properties of weld metal, and a gas shielded arc welding method.SOLUTION: A metal flux-cored wire for welding comprises a steel sheath and flux. In mass percentage based on the total mass of the wire, the steel sheath and the flux contain, in total, C: 0.13-0.25%, Si (excluding Si contained as Si oxide): 0.1-1.2%, Mn: 0.5-2.0%, S: 0.020-0.050%, and P: 0.03% or less. In mass percentage based on the total mass of the wire, the flux contains metal fluoride: a total of 0.003-0.120% in terms of F, and Na oxide and / or K oxide: a total of 0.02-0.10% in terms of Na2O and / or K2O. The balance is Fe and impurities. There is also provided a gas shielded arc welding method using the same.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a metal-based flux-cored welding wire and a gas-shielded arc welding method. [Background technology]

[0002] Flux-cored wires for gas-shielded arc welding are highly efficient and have excellent welding workability, and are widely used in fields such as architecture, steel frames, and marine structures. Metal-based flux-cored wires in particular produce less slag than rutile-based or basic-based flux-cored wires, which produce a lot of slag, and the slag removal work in continuous multi-pass welding is simple, so they are preferred for use under conditions of continuous multi-pass welding inside a groove.

[0003] In particular, metal-based flux-cored wire for gas-shielded arc welding using Ar-CO2 mixed gas produces smaller droplets than solid wire or metal-based flux-cored wire for gas-shielded arc welding using CO2 gas, making it less likely to generate large spatter. This reduces the amount of spatter adhering to the weld or welding torch nozzle, reducing the amount of spatter removal required. Furthermore, the degree of slag formation due to oxidation of alloying agents such as Mn and Si and deoxidizers is low, reducing the amount of slag generated. Furthermore, reducing the oxygen content of the weld metal effectively improves the low-temperature toughness of the weld metal, making it widely used.

[0004] Various types of metal-based flux-cored wires for gas-shielded arc welding using Ar-CO mixed gas have been developed. For example, Patent Document 1 discloses a flux-cored wire for gas-shielded arc welding using a mixed gas that produces less slag and can produce flat beads in horizontal fillet welding. Furthermore, Patent Document 2 discloses a flux-cored wire for gas-shielded arc welding that contains a large amount of alloy powder and uses a mixed gas that has excellent low-temperature toughness. Patent Document 3 discloses a flux-cored wire for gas-shielded arc welding that uses a mixed gas that has good arc stability, good welding workability such as a small amount of spatter, and excellent low-temperature toughness. Patent Document 4 discloses a metal-based flux-cored wire for gas-shielded arc welding using an Ar-CO mixed gas, which is used in short arc welding and spray arc welding to produce extremely small amounts of slag and spatter, obtain a good bead shape, and also provide a weld metal with good low-temperature toughness. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-197991 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-144516 [Patent Document 3] Japanese Patent Publication No. 2020-203302 [Patent Document 4] Patent No. 5207994 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the flux-cored wires described in Patent Documents 1 and 2 have low carbon content and no specified sulfur content, resulting in a large amount of slag. Furthermore, the slag spreads thinly over the bead, making it difficult to remove, requiring time for removal, and resulting in an uneven bead appearance. Furthermore, when multiple passes are performed without removing the slag, the area of ​​slag covering the bead increases. Therefore, if the consumable electrode (wire) comes into contact with the slag when starting the arc for the next pass, no current flows and no arc occurs. To generate an arc, the slag must be removed from the area where the wire is in contact. In the case of automatic welding, this process results in significant time loss and increased manufacturing costs. Furthermore, since the flux-cored wires described in Patent Documents 2 and 3 contain Ti, a large amount of Ti oxide is produced, resulting in a large amount of slag, which takes a long time to remove. Furthermore, the flux-cored wire described in Patent Document 4 also has a small amount of C and tends to produce a large amount of slag, so there is room for further improvement.

[0007] The present disclosure has been made in view of the above-mentioned problems, and has an object to provide a metal-based flux-cored welding wire and a gas-shielded arc welding method that are excellent in welding workability such as arc stability, amount of spatter generated, amount of slag generated, and bead shape, and that are also excellent in resistance to blowhole defects and cracking, and that produce a deposited metal with good mechanical properties. [Means for solving the problem]

[0008] The gist of the present disclosure for solving the above problems is as follows. <1> A metal-based flux-cored welding wire including a steel sheath and a flux filled in the steel sheath, The total mass of the steel sheath and flux is expressed as a percentage by mass of the total wire mass. C: 0.13~0.25%, Si (excluding Si contained as Si oxide): 0.1 to 1.2% Mn: 0.5 to 2.0%, S: 0.020 to 0.050%, and P: 0.03% or less, Furthermore, in the flux, the mass percentage relative to the total mass of the wire is: Metal fluorides: 0.003 to 0.120% in total F equivalent value, and One or more of Na oxide and K oxide: Contains 0.02 to 0.10% in total of NaO equivalent and KO equivalent, The remainder of the wire is a steel sheath and Fe and impurities contained in the flux. <2> The flux contains 0.20% or less of silicon oxide (SiO2 equivalent) in total, expressed as a percentage by mass relative to the total mass of the wire. <1> The welding metal-based flux-cored wire according to claim 1. <3> The value calculated by the following formula 1 is 0.47 to 1.90. <1> or <2> The welding metal-based flux-cored wire according to claim 1. Equation 1: (10[S]+3[C]) / [Mn] In the formula 1, the [element symbol] indicates the mass % of each element contained in the steel sheath and flux relative to the total mass of the wire. <4> In mass % relative to the total mass of the wire, the total of the steel sheath and flux contains one or two of Ni: 1.5% or less and B: 0.010% or less. <1> ~ <3> 10. The metal-based flux-cored welding wire according to claim 9, wherein the welding wire is a metal-based flux-cored wire. <5> In mass % relative to the total mass of the wire, the total of the steel sheath and flux contains one or more of Mo: 0.30% or less, Cu: 0.50% or less, Cr: 0.05% or less, V: 0.05% or less, Mg: 0.05% or less, Ti: 0.05% or less, and Al: 0.05% or less. <1> ~ <4> 10. The metal-based flux-cored welding wire according to claim 9. <6> <1> ~ <5> 1. A gas-shielded arc welding method, in which welding is performed using the metal-based flux-cored welding wire according to any one of the above items and a shielding gas. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a metal-based flux-cored welding wire and a gas-shielded arc welding method that are excellent in welding workability such as arc stability, amount of spatter generated, amount of slag generated, and bead shape, as well as excellent in resistance to blowhole defects and cracking, and produce a deposited metal with good mechanical properties. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment that is an example of the present disclosure will be described, but the metal-based flux-cored welding wire and gas-shielded arc welding method according to the present disclosure are not limited to the embodiment described below. In this disclosure, when a numerical range expressed using "to" is not preceded or followed by "greater than" or "less than," it means a range that includes these numerical values ​​as the lower and upper limits. When "to" is preceded or followed by "greater than" or "less than," it means a range that does not include these numerical values ​​as the lower or upper limit. In the present specification, the upper limit of a numerical range described in stages may be replaced by the upper limit of another numerical range described in stages or by a value shown in an example. Also, the lower limit of a numerical range may be replaced by the lower limit of another numerical range described in stages or by a value shown in an example. With respect to the content, "%" means "% by mass" unless otherwise specified. Furthermore, when the content (%) is specified with only an upper limit of "not more than ____%" without specifying a lower limit, it means that the content may be in the range of more than 0% to the upper limit.

[0011] In order to solve the above problems, the present inventors have conducted extensive research to obtain a metal-based flux-cored wire for welding that is excellent in welding workability such as arc stability, amount of spatter generated, amount of slag generated, and bead shape, and that is also excellent in resistance to blowhole defects and cracking, and that produces a weld metal with good mechanical properties. As a result, they have found that by adjusting the S and C contents of the metal-based flux-cored wire to appropriate levels, a slag coagulation effect can be obtained, and an effect of improving the bead appearance can be obtained.

[0012] <Metallic flux-cored welding wire> The metal-based flux-cored welding wire according to the present disclosure includes a steel sheath and a flux filled in the steel sheath, and the total mass of the steel sheath and the flux, in mass % relative to the total mass of the wire, is: C: 0.13~0.25%, Si (excluding Si contained as Si oxide): 0.1 to 1.2% Mn: 0.5 to 2.0%, S: 0.020 to 0.050%, and P: Contains 0.03% or less, Furthermore, in the flux, the mass percentage relative to the total mass of the wire is: Metal fluorides: 0.003 to 0.120% in total F equivalent value, and One or more of Na oxide and K oxide: Contains 0.02 to 0.10% in total of NaO equivalent and KO equivalent, The balance consists of Fe and impurities contained in the steel sheath and flux.

[0013] The reasons for limiting the component composition of the metal-based flux-cored welding wire of the present disclosure will be explained below. Note that the content of each component in the present disclosure is expressed as mass% relative to the total mass of the wire, and is simply expressed as %. The metal-based flux-cored welding wire according to the present disclosure contains, as essential components, one or more of C, Si (excluding Si contained as Si oxide), Mn, S, P, metal fluoride, and Na oxide and K oxide. The metal-based flux-cored welding wire according to the present disclosure may contain Si oxide in the flux.

[0014] [Total of steel sheath and flux: C: 0.13 to 0.25%] C has the effect of improving the strength of the weld metal. C also has the effect of adjusting the amount of slag produced. If C is less than 0.13%, the amount of slag produced increases. On the other hand, if C is more than 0.25%, hot cracking occurs. Therefore, the total C content of the steel sheath and flux is set to 0.13 to 0.25%. C can be added from the components contained in the steel sheath, as well as from metal powder and alloy powder from the flux. The C content is preferably 0.13 to 0.20%.

[0015] [Si content in steel sheath and flux combined (excluding Si contained as Si oxides): 0.1 to 1.2%] Si has the effect of improving the strength and toughness of the weld metal. It also has the effect of increasing the viscosity of the molten metal, improving the bead appearance and shape. Furthermore, Si has the effect of adjusting the amount of slag production. If the Si content is less than 0.1%, the bead appearance and bead shape deteriorate. Also, the resistance to blowhole defects decreases. On the other hand, if the Si content exceeds 1.2%, excessive Si is retained in the weld metal, increasing the strength of the weld metal and decreasing the low-temperature toughness. Furthermore, if the Si content exceeds 1.2%, the amount of slag produced increases. Therefore, the total Si content of the steel sheath and flux is set to 0.1 to 1.2%. Note that, in the present disclosure, the Si content does not take into account Si contained as Si oxides, if any. In addition to the components contained in the steel sheath, Si can be added from the flux as metallic Si, Fe-Si, Fe-Si-Mn, or other alloy powders. The Si content is preferably 0.4 to 1.1%.

[0016] [Mn content in steel sheath and flux: 0.5-2.0%] Mn acts as a deoxidizer and also has the effect of improving the strength and low-temperature toughness of the weld metal. If the Mn content is less than 0.5%, the strength and low-temperature toughness of the weld metal will decrease. On the other hand, if the Mn content exceeds 2.0%, Mn will be excessively retained in the weld metal, increasing the strength of the weld metal and decreasing the low-temperature toughness. In addition, the amount of slag produced will increase. Therefore, the total Mn content in the steel sheath and flux is set to 0.5 to 2.0%. Note that Mn can be added from the components contained in the steel sheath, as well as from alloy powders such as metallic Mn, Fe-Mn, and Fe-Si-Mn from the flux. The Mn content is preferably 0.8 to 1.8%.

[0017] [Sulfur content in steel sheath and flux: 0.020-0.050%] Sulfur reduces the surface tension of the molten pool during welding, thereby changing the flow of molten metal and making it easier for slag to aggregate. Aggregation of slag facilitates slag separation after welding. Furthermore, a good bead appearance can be obtained after slag separation. If the S content is less than 0.020%, the molten slag does not aggregate and adheres in a fine, sparsely dispersed state, resulting in poor bead appearance. On the other hand, if the S content exceeds 0.050%, the low-temperature toughness of the weld metal decreases. Furthermore, if the S content exceeds 0.050%, hot cracking is more likely to occur in the weld metal. Therefore, the total S content of the steel sheath and flux is set to 0.020 to 0.050%. In addition to the components contained in the steel sheath, S can be added from the flux via metal powder, alloy powder, iron sulfide, etc. The S content is preferably 0.022 to 0.040%.

[0018] [P: 0.03% or less in total for steel sheath and flux] P is one of the main elements that causes hot cracking in the weld metal, and is an impurity contained in trace amounts in the raw materials of the steel sheath and flux. Therefore, the P content is limited to 0.03% or less.

[0019] [Metal fluorides in flux: 0.003 to 0.120% in total F converted value] Metal fluorides have the effect of stabilizing the arc. If the total F-equivalent value of the metal fluorides is less than 0.003%, the arc will be weak and unstable. On the other hand, if the total F-equivalent value of the metal fluorides exceeds 0.120%, the arc will be too strong and the amount of spatter will increase. Therefore, the total F-equivalent value of the metal fluorides is set to 0.003 to 0.120%. Note that metal fluorides can be added from CaF2, NaF, LiF, MgF2, K2SiF6, Na3AlF6, AlF6, etc., and the F-equivalent value is the total F content contained in these. The total F-equivalent value of the metal fluorides is preferably 0.003 to 0.030%. Note that even though Si, Mg, and Al are constituent elements of metal fluorides, if they are contained in the wire, they turn into slag during welding, increasing the amount of slag, so it is preferable that their contents are low. Therefore, Si, Mg, and Al, which can constitute metal fluorides, are also considered as elements that can be contained in the flux-cored wire according to the present disclosure, with Si (excluding Si contained as Si oxides): 0.1 to 1.2%, Mg: 0.05% or less, and Al: 0.05% or less. On the other hand, other metal elements such as Ca, Na, Li, and K, which can constitute metal fluorides, are considered only as metal fluorides.

[0020] [One or more of sodium oxides and potassium oxides in the flux: 0.02 to 0.10% in total of Na2O equivalent and K2O equivalent] Na oxide and K oxide act as arc stabilizers, improving arc stability. If the total of the Na2O equivalent and K2O equivalent values ​​of one or more Na oxides and K oxides is less than 0.02%, the arc becomes unstable, resulting in increased spatter generation. On the other hand, if the total of the Na2O equivalent and K2O equivalent values ​​of one or more Na oxides and K oxides exceeds 0.10%, the arc length becomes longer, the arc becomes unstable, and the spatter generation increases. Therefore, the total of the Na2O equivalent and K2O equivalent values ​​of one or more Na oxides and K oxides in the flux is set to 0.02-0.10%. Na oxide and K oxide can be added in the form of powders such as solid components of water glass composed of sodium silicate and potassium silicate, potassium feldspar, and Na2Ti3O7. The total of the Na2O equivalent and K2O equivalent values ​​of one or more Na oxides and K oxides is preferably 0.03-0.07%.

[0021] [Si oxides in flux: SiO2 equivalent total of 0.20% or less] Si oxides may be included in the flux to improve the bead toe conformity and improve the bead appearance and shape. However, the amount of slag produced and the oxygen content in the weld metal increase, so the Si oxide content must be limited. If the total Si oxide content in terms of SiO2 exceeds 0.20%, the oxygen content in the weld metal increases and low-temperature toughness decreases. Therefore, the total Si oxide content in terms of SiO2 must be 0.20% or less. Si oxide can be added from the solid components of water glass, which is made from silica sand, orthoclase, sodium silicate, and potassium silicate, etc., from the flux. The total Si oxide content in terms of SiO2 is preferably 0.15% or less.

[0022] In the metal-based flux-cored welding wire according to the present disclosure, the value calculated by the following formula 1 preferably satisfies 0.47 to 1.90.

[0023] [Equation 1: (10[S] + 3[C]) / [Mn] is 0.47 to 1.90] In formula 1, the [element symbol] represents the mass % of each element contained in the steel sheath and flux relative to the total mass of the wire. If the value calculated by formula 1 is less than 0.47, the amount of slag generated will be slightly large. On the other hand, if the value calculated by formula 1 exceeds 1.90, the bead appearance will be slightly deteriorated. Therefore, the value calculated by formula 1 is preferably 0.47 to 1.90. The value calculated by formula 1 is preferably 0.50 to 1.30.

[0024] The metal-based flux-cored welding wire according to the present disclosure may contain, in addition to the above elements, one or both of Ni and B in place of a portion of Fe. When these elements are contained, the respective contents are as follows.

[0025] [Ni: 1.5% or less in total for steel sheath and flux] Ni has the effect of further improving the low-temperature toughness of the weld metal. However, if Ni exceeds 1.5%, the strength of the weld metal becomes excessive and hot cracking becomes more likely to occur. Therefore, the total Ni content of the steel sheath and flux is set to 1.5% or less. To obtain the effect of improving low-temperature toughness, Ni is preferably 0.3% or more. To further improve toughness at low temperatures, Ni is preferably 0.5% or more. In addition to being a component contained in the steel sheath, Ni can be added from metallic Ni from the flux, metal powder such as Fe-Ni, etc.

[0026] [B: 0.010% or less in total for steel sheath and flux] B has the effect of further improving the low-temperature toughness of the weld metal. However, if B exceeds 0.010%, the strength of the weld metal becomes excessive and hot cracking becomes more likely to occur. Therefore, the total B content of the steel sheath and flux is set to 0.010% or less. To obtain the effect of B improving the low-temperature toughness of the weld metal, it is preferable that B be 0.004% or more. B can be added from alloys such as Fe-B, borax, and colemanite, or from oxides.

[0027] The metal-based flux-cored welding wire according to the present disclosure may further contain other elements in addition to the above elements in place of a portion of Fe. For example, the metal-based flux-cored welding wire according to the present disclosure may contain one or more of Mo, Cu, Cr, V, Mg, Ti, and Al within the following content ranges. When these elements are contained in the metal-based flux-cored welding wire, the respective contents shall be as follows.

[0028] [Mo: 0.30% or less in total for steel sheath and flux] Mo may not be contained, or may be contained to improve tensile strength, but if contained in excess, the tensile strength of the welded part becomes too high and the toughness decreases. Therefore, the Mo content is set to 0.30% or less.

[0029] [Cu content of steel sheath and flux combined: 0.50% or less] Cu may not be contained, or it may be contained by applying a Cu-based plating to the steel sheath to improve tip wear resistance. Applying a Cu-based plating to the steel sheath can suppress tip wear caused by the wire passing through the inside of the tip (insertion hole). However, if the wire contains excessive Cu, hot cracking is more likely to occur. Therefore, the Cu content should be 0.50% or less. Note that if the steel sheath is coated with a Cu-based plating, the plating is considered to be part of the steel sheath.

[0030] [Cr: 0.05% or less in total for steel sheath and flux] Cr may or may not be contained, but while Cr increases strength, excessive Cr content reduces the toughness of the weld. Therefore, the Cr content is set to 0.05% or less.

[0031] [V: 0.05% or less in total for steel sheath and flux] V may or may not be contained, but while V increases strength, excessive V content reduces the toughness of welds. Therefore, the V content is set to 0.05% or less.

[0032] [Mg: 0.05% or less in total for steel sheath and flux] Although Mg may be added or not, it is preferable not to add Mg because it increases the amount of slag produced and deteriorates welding workability. If Mg is added, the Mg content should be 0.05% or less.

[0033] [Ti: 0.05% or less in total for steel sheath and flux] Although Ti may or may not be contained, it is preferable not to contain Ti because Ti generates Ti oxides, which increases the amount of slag produced and deteriorates welding workability. If Ti is contained, the Ti content is preferably 0.05% or less.

[0034] [Al: 0.05% or less in total for steel sheath and flux] Although Al may or may not be contained, it is preferable not to contain Al because Al increases the amount of slag produced and deteriorates welding workability. If Al is contained, it is preferable that the Al content be 0.05% or less.

[0035] The remainder of the metal-based flux-cored welding wire of the present disclosure is Fe and impurities, such as Fe in the steel sheath, iron powder in the flux, and the Fe content and impurities in iron alloy powder such as Fe-Mn, Fe-Si-Mn, and Fe-Ni alloys.

[0036] The flux filling rate is not particularly specified, but is preferably 8 to 20 mass % with respect to the total mass of the wire from the viewpoint of productivity.

[0037] The diameter of the metal-based flux-cored welding wire according to the present disclosure is not particularly limited, but is, for example, 1.0 to 2.0 mm.

[0038] <Gas shielded arc welding method> Next, a gas-shielded arc welding method using the metal-based flux-cored welding wire according to the present disclosure will be described. The metal-based flux-cored welding wire according to the present disclosure can be suitably used in a welding method in which a shielding gas is used during welding.

[0039] That is, the gas-shielded arc welding method according to the present disclosure is a gas-shielded arc welding method in which welding is performed using the metal-based flux-cored welding wire according to the present disclosure and a shielding gas.

[0040] Known shielding gases can be used during welding. For example, 100% CO2 tends to generate slag, while 100% Ar tends to reduce arc stability. To reduce the amount of oxygen in the weld metal, a mixed gas of Ar-5 to 25% by volume CO2 is preferably used, but is not limited to this. The gas-shielded arc welding method according to the present disclosure may be, but is not particularly limited to, pulse welding. [Example]

[0041] The effects of the present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to the following examples.

[0042] [Manufacturing of metal flux-cored welding wire] First, JIS G3141:2017 SPCC strip steel was used for the steel sheath, which was formed into a U-shape and filled with flux that had been dried to thoroughly remove moisture. Then, seamless wires in which the seams of the steel sheaths were welded, and jointed wires in which the steel sheaths were crimped together were formed into pipes and drawn to produce prototype flux-cored wires with a wire diameter of 1.2 mm and various main compositions as shown in Table 1. The flux filling rate was set to 10 to 18 mass%. In Table 1, values ​​outside the range of the present disclosure, including optional requirements, are underlined. Also, blank spaces in Table 1 indicate that the element was not intentionally added. Also, wire containing Cu means that the steel sheath is plated. The metal fluorides used were one or more of CaF2, NaF, LiF, MgF2, K2SiF6, Na3AlF6, and AlF3, and when Si, Mg, and Al were contained as metal fluorides, they were also included in the content of Si, Mg, and Al, respectively.On the other hand, Si contained as Si oxide was not included in the Si content.

[0043] [Table 1]

[0044] The meanings of the shielding gas symbols are as follows: C:CO2 M: Ar-20% CO2

[0045] [evaluation] Using the wire manufactured as described above, flat welding workability and mechanical properties of the weld metal were evaluated. For welding workability, welding was performed in accordance with JIS Z3111:2005 using 20mm thick steel plates specified in JIS G3126:2015 SLA365, under the welding conditions shown in Table 2. Arc stability, amount of spatter generated, amount of slag generated, and bead appearance and shape were visually inspected, and the presence or absence of porosity defects and hot cracking was also inspected.

[0046] [Table 2]

[0047] (Arc stability) Arc stability indicates the degree of arc stability. A stable arc means that there is little fluctuation in the length of the arc generated between the wire tip and the steel sheet. If the arc length fluctuates too much, the amount of spatter increases and the bead appearance deteriorates. Arc stability was judged visually during welding.

[0048] (amount of spatter generated) The amount of spatter generated was determined by collecting the spatter generated when welding was performed for 1 minute on a JIS G 3106:2017 SM490A steel plate (plate thickness 12 mm) using the current, voltage, welding speed, and shielding gas shown in Table 2 in a copper collection box and measuring its weight. The amount of spatter generated was measured five times, and an average value of 1.5 g or less was considered good. Low: spatter generation amount is 1.5g or less High: The amount of spatter generated exceeds 1.5g

[0049] (Amount of slag produced) The amount of slag generated was evaluated based on the area ratio of the slag on the bead after measuring the amount of spatter generated. Very little: slag area ratio is 5% or less Low: Slag area ratio is over 5% and 10% or less High: Slag area ratio is over 10%

[0050] (Bead appearance and shape) Regarding the inspection of bead appearance and shape, if the bead appearance and shape are beautiful and uniform, it is judged as good, and if the bead appearance and shape are partly or entirely irregular and unstable, it is judged as poor. In this example, the bead appearance and shape were judged to be good or bad by visual observation. The specific criteria for judging the bead appearance and shape were that if there was even one undercut or overlap, it was judged to be bad, and if there were any other, it was judged to be good.

[0051] (Porosity defect resistance) The bead surface was visually inspected for the presence or absence of porosity defects such as pits. If even one porosity defect appeared after each welding pass, it was rated as "present."

[0052] <Weld metal test> The weld metal test was performed using 20mm thick steel plates specified in JIS G3126:2015 SLA365, welding in accordance with JIS Z3111:2005, and the test was conducted based on the method of "JIS Z 2343-1:2017 Non-destructive testing - Penetrant testing - Part 1."

[0053] (crack resistance) If even one crack was found on the bead surface in the weld metal test, it was marked as "present." After each welding pass, the presence or absence of hot cracks was visually inspected.

[0054] (chip wear resistance) After the weld metal test, the wear state of the tip was visually confirmed and evaluated. Very good: almost no wear Good: slight wear

[0055] (mechanical properties) Tensile test (A0 type) and impact test (V-notch test piece) specimens were taken from the center of the weld metal in the thickness direction, and mechanical tests were conducted. In the tensile test, a 0.2% yield strength of 460 MPa or more and a tensile strength of 540 to 680 MPa were considered good. The impact test was evaluated by a Charpy impact test (vE-40) at -40°C, and a specimen with an average absorbed energy of 60 J or more after three repeated tests was considered good. For reference, a Charpy impact test (vE-60) was also conducted at -60°C. These results are summarized in Table 3. If all evaluation items were good or better, the overall evaluation was marked with a circle, and if even one item was not good, it was marked with an X.

[0056] [Table 3]

[0057] In Table 3, wires W1 to W20, W31, and W32 are examples of the present invention, while wires W21 to W30 are comparative examples. The wires W1 to W20, W31, and W32, which are examples of the present invention, had appropriate amounts of C, Si, Mn, S, and P in the steel sheath and flux of the metal-based flux-cored wires combined, and the total F-equivalent values ​​of metal fluorides in the flux and the total NaO-equivalent values ​​and KO-equivalent values ​​of one or more sodium oxides and potassium oxides were appropriate. Therefore, these examples of the present invention had stable arcs, low spatter generation, low slag generation, good bead appearance and shape, and no porosity or hot cracking. Furthermore, these examples of the present invention had good mechanical properties of the deposited metal, such as 0.2% proof stress, tensile strength, and absorbed energy.

[0058] The comparative wires W21 to W30 failed in one or more evaluation items because the total components of the steel outer sheath and flux of the metal-based flux-cored wires were outside the range specified in this disclosure.

Claims

1. A metal-based flux-cored welding wire including a steel sheath and a flux filled in the steel sheath, The total mass of the steel sheath and flux is expressed as a percentage by mass of the total wire mass. C: 0.13-0.25%, Si (excluding Si contained as Si oxide): 0.1 to 1.2% Mn: 0.5-2.0%, S: 0.020 to 0.050%, and P: 0.03% or less, Furthermore, in the flux, in mass % relative to the total mass of the wire, Metal fluorides: 0.003 to 0.120% in total in terms of F; and One or more of sodium oxide and potassium oxide: Na ２ O conversion value and K ２ Contains 0.02 to 0.10% in total converted to O, The balance is composed of Fe and impurities contained in the steel sheath and flux, A metal-based flux-cored welding wire having a value calculated by the following formula 1 of 0.47 to 1.

90. Formula 1: (10[S]+3[C]) / [Mn] In the formula 1, the [element symbol] represents the mass % of each element contained in the steel sheath and flux relative to the total mass of the wire.

2. In the flux, Si oxide: SiO ２ 2. The welding metal-based flux-cored wire according to claim 1, containing 0.20% or less in total converted value.

3. 3. The metal-based flux-cored welding wire according to claim 1, wherein the total of the steel sheath and the flux contains, in mass % relative to the total mass of the wire, one or both of Ni: 1.5% or less and B: 0.010% or less.

4. In mass % relative to the total mass of the wire, the total of the steel sheath and flux, Mo: 0.30% or less, Cu: 0.50% or less, Cr: 0.05% or less, V: 0.05% or less, Mg: 0.0 4. The welding metal-based flux-cored wire according to claim 1, further comprising one or more of: Cr: 0.5% or less, Ti: 0.05% or less, and Al: 0.05% or less.

5. A gas-shielded arc welding method, comprising: welding using the metal-based flux-cored welding wire according to any one of claims 1 to 4 and a shielding gas.

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